Durnolf is going to attempt to do way too many things at once. Starting with:

fast dismount with guidance:1d20 + 8 ⇒ (7) + 8 = 15

boo.

Durnolf takes his sweet time getting out of the saddle into the lady Ardoc's square., and the rest of this should work but I'm not 100% on it. Durnolf deliberately provokes the snake, trying to distract it by pulling out a vial of sweet minty cure light while commanding Ruckus to drag Elizabeth to safety past him (work trick to d27). If possible, Durnolf then takes a 5 ft step out of the way back to where he started.

Hmm...I'm afraid that while this was effective, Durnolf was likely caught in the blast as well. Dismount is the move action. Land in current square. 5' step into Elizabeth's square. Standard action to draw potion. Out of actions. Correct?

I was under the assumption that I'd dismount into Elizabeth's, as I didn't think I could share space with Ruckus since he's still up and about, but I can see yours too, and it's totally your call as GM.

Better bring Elizabeth back on her feet quick. She will need them, whether she wil make a stand with us, or run for it with us, Gunder thinks. Without waiting for the others to make their decision, he squeezes past them to get to Elizabeth. Never thought I would risk my life to save an Ardoc.He casts Cure light wounds on her twice. Assuming there is enough time before bone horror reaches the top of the pit.

"That serpent was some sort of guardian. Such an odd place. The naginis are liars instead of guardians, and in their place are some form of construct. The entryway it was guarding must lead to something important. I hope we didn't inadvertently aid the necromancer in obtaining something," says Garuneh.

"Don't mention it, Elizabeth. You should rest now. Unfortunately this seems to be neither the right time nor the right place to rest. Do you think you can walk?"

Gunder feels most uneasy about the idea of having played into the necromancer's hands. "I wish you hadn't just said that. We should at least close that hidden door and hope that the necromancer won't notice it. There's not enough time to do much more now, I fear."

back at the base camp:

Gunder is relieved when they reach the base camp and secure the last door behind them.

After making sure everyone is okay, he turns his mind to eating. (I still have one spell left, if anyone needs to be cured.)

"That could have gone worse, I suppose. It is unfortunate we alerted whatever is down at the bottom of that pit. At least we managed to get away without serious injury." Aldous idly flips through his spellbook and feeds crumbs to Dragon.

"I will have some crispy darkmantle skin fried in its own fat, and some grilled spider legs. Something to spice up these rations. And I'll at least try a small bite of the darkmantle meat, I think Elizabeth here has a point about fat carrying flavor. Besides, you never know whether something is delicious until you tried."
Gunder hands some delicious darkmantle and spider legs to Elizabeth, Durnolf and anyone else willing to try.

I'm ready to go to bed and then continue to disturb some more ancient evil. When going back north, Gunder will cast Guidance and Virtue on everybody at every door and intersection. Just in case that thing from the pit is waiting for us somewhere.

Gunder nibbles on his spider leg happily. "You should try the webs, Elizabeth. Maybe they are more to your liking. There's this fancy Goblin restaurant in Hospice. Of course it's tailored to the tourists' taste - not very authentic Goblin cuisine. But this kind of reminds me of the food they serve there."